For many different purposes it is desirable to have a ring spun yarn with a distinct sheath/core configuration. For instance it is desirable to be able to produce ring spun yarns having different fibers in the core and the sheath which has most of the advantages of both the core and the sheath fibers. For instance in the production of yarn for sports shirts, it is desirable to have a yarn that has the feel of cotton, or like natural fibers, but has better strength. Also in the production of denim, and other heavyweight fabrics for pants and uniforms, it is desirable to have sheath/core configuration yarns so that the fabric has the feel imparted by one fiber, but the strength imparted by another. There have been many proposals for procedures in order to accomplish these results, which have met with varying degrees of success, but still there are few commercially acceptable ring spun sheath/core yarns.
According to the present invention it has been recognized that it is desirable to act upon the fibers which are to form the core and the sheath of a ring spun yarn in such a way as to maintain good core cohesiveness throughout processing, and to maintain the core and sheath fibers as distinct as possible. The ring spun yarn produced according to the invention has the core completely covered by the sheath fibers, and by varying the percentages of sheath/core fibers one can achieve different tactile and functional properties. By practicing the invention it is possible to optimize the fabric properties according to end use requirements.
According to the present invention a method of producing a roving having a sheath/core configuration, utilizing a drafting apparatus comprising front and back rolls with an apron therebetween, is provided. The method comprises the steps of: (a) Feeding a sliver of first fibers and a roving of second fibers to the drafting apparatus so that the roving of second fibers is at the center line of, and on top of, the sliver of first fibers. The first and second fibers have distinctly different properties. For instance the sheath fibers can be soft natural fibers, such as cotton or wool, while the core fibers can be synthetic fibers, such as polyester, nylon, and other synthetic fibers in staple form. (b) The roving and sliver are passed together through the rear rolls, apron, and front rolls of the drafting apparatus to produce a drafted composite sliver. Then, (c) mechanical twist is imparted to the drafted composite sliver by a roving frame to produce a roving having a core and sheath covering the core.
By carefully controlling the fiber cohesiveness, one can ensure that the core and the sheath remain entirely distinct. Core cohesiveness can be maintained by: particularly controlling the twist of the roving of second fibers (e.g. so that it has a twist multiple of about 0.25-0.80 turns per inch); and/or applying a finish to the roving of second fibers so that it has high friction than the first fibers; and/or passing the sliver and roving through a trumpet so as to precisely control the placement of the roving on top of the sliver so that the roving is at the exact center line of the sliver, and has no opportunity to move off the exact center line before passing to the rear rolls. Once the sliver and roving pass together to the rear rolls, the drafting apparatus will have a tendency to move the first fibers of the sliver to completely surround the second fibers of the core, and not intermix them. As the two fiber bands move out of the front roll, the twisting action of the flyers will cause the complete covering of the sheath fibers around the core fibers.
According to the method of the present invention, it is possible to produce spun yarn from the composite roving produced above merely by subjecting the roving to another conventional draft stage, and then mechanically spinning it on a spinning frame. Typically the drafting in step (b) above would provide a draft ratio of about 10-1, while the drafting in the second drafting stage, prior to yarn spinning, would be at a draft ratio of about 6-1.
The invention also comprises particular apparatus for producing the sheath/core yarn. The apparatus includes conventional components for producing a roving from sliver, and also comprises a support for the roving of second fibers, and a trumpet between the support and the rear rolls of the drafting apparatus. The trumpet guides the roving and sliver together to the rear rolls of the drafting apparatus so that they are in the particular desired arrangement, with the roving on top of the sliver and at the exact center line thereof. The trumpet includes a sliver guiding element which necks down from the sliver supply to the drafting apparatus, and has a generally oval shaped opening with a 3-1 width to height ratio through which the sliver exits. The trumpet also comprises a roving guiding element mounted on top of the sliver guiding element, for guiding the roving so that it is disposed at the exact center line of, and on top of, the sliver and so that the roving has no chance to move before the roving and sliver go together to the nip of the rear rolls of the drafting apparatus.
It is the primary object of the present invention to provide an improved method and apparatus for producing sheath/core yarn, where the yarn has a cohesive core and the sheath completely covers the core. This and other objects of the invention will become clear from an inspection of the detailed description of the invention, and from the appended claims.